The present invention relates to detection apparatus and, more particularly, to apparatus for detecting the presence and position of individual wheel-axles of railroad cars.
As background material for an understanding of the apparatus and technique of the present invention, reference may be made to the following patents: British Pat. No. 767,724; U.S. Pat. No. 3,697,745; and U.S. Pat. No. 4,058,279, the last named being assigned to the assignee of the present invention and in which there is described a system or apparatus for detecting wheel "flats". In accordance with such system, a pair of individual test sections is established and a pair of loops for detecting or sensing the wheel "flats" is correlated with the respective test sections. Each of the loops includes a pair of pick-up coils connected in opposing polarity such that under "no wheels present" conditions the voltage produced in each of the pair of coils is substantially identical such that a zero net output voltage is produced in a detection loop; whereas, when a wheel-axle is present in one of the test sections, one of the pair of coils is "shorted out" such that the output voltage abruptly rises for that detection loop. However, the output voltage falls again whenever a wheel flat occurs.
Unlike the system of the aforenoted U.S. Pat. No. 4,058,279, the system of the present invention is directed to detecting the presence of individual wheel-axles and of providing a reasonably precise indication of the position within such test or detecting section.
Accordingly, it is a primary object of the present invention to provide apparatus that will permit detection of the presence of wheel-axles in a detecting section.
An ancillary object is to provide a convenient measurement for ascertaining the position within the detecting section of the wheel-axles.
In fulfillment of the above-noted objects, a primary feature of the present invention resides in a system for detecting the presence and position of railroad car wheels in which a transmitter having a high-frequency output is connected to a pair of rails which, together with suitable shorting means, constitute a first loop for the flow of the high frequency current from said transmitter. A second loop extends in close proximity to said first loop and a sensing means associated with the loops functions to sense the changes in fields resulting when a wheel-axle combination comes into the test or detection zone.
Preferably, the sensing means takes the form of a pick-up coil positioned adjacent one of the loops. By reason of countercurrent flows established in the two loops, the fields produced by the loop currents are normally canceled and minimized in the vicinity of the pick-up coil. However, when a wheel-axle is present in a test or detection zone, the pick-up coil produces a relatively sharp position response with respect to that wheel or wheel-axle combination.
In a preferred embodiment the transmitter is connected in series with both of the current loops and is further so connected so that the loops are normally subdivided into two equal portions with respect to a center line; additionally, the pick-up coil is positioned to be aligned along that center line.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawing, wherein like parts have been given like numbers.